Low spin golf ball

ABSTRACT

A golf ball is disclosed that comprises a core and a cover disposed about the core. Preferably, the cover includes at least one high acid ionomer resin that comprises a copolymer of greater than 16% by weight of an acrylic acid, and an alpha olefin of which about 10 to about 90% of the carboxyl groups of the copolymer are neutralized with a metal cation.

This application is a continuation of application Ser. No. 09/102,342,filed Jun. 22, 1998, which is a continuation of application Ser No.08/716,016, field Sep. 19, 1996 (now U.S. Pat. No. 5,820,489), which isa divisional of application Serial No. 08/255,442, filed Jun. 8, 1994(abandoned), which is a continuation of application Ser. No. 08/054,406,filed Apr. 28, 1993 (now U.S. Pat. No. 5,368,304); and further whereinapplication Ser. No. 09/102,342 is a continuation-in-part of applicationSer. No. 08/649,050, filed May 16, 1996 (abandoned) which is adivisional of application Ser. No. 08/493,089, filed Jun. 21, 1995 (nowU.S. Pat. No. 5,688,869) which is a continuation of application Ser. No.07/981,751, filed Nov. 25, 1992 (abandoned) which is acontinuation-in-part of application Ser. No. 07/901,660, filed Jun. 19,1992 (abandoned).

FIELD OF THE INVENTION

The present invention relates to golf balls and, more particularly, toimproved two-piece golf balls having low spin rates. The improvement inthe golf balls results from a combination of a softened polybutadienecore and a hard cover made from blends of one or more specific hard,high stiffness ionomers. The combination of a soft core and a hard coverleads to an improved golf ball having a lower than anticipated spin ratewhile maintaining the resilience and durability characteristicsnecessary for repetitive play.

In an additional embodiment of the invention, the spin rate is furtherreduced by decreasing the weight of the softened polybutadiene corewhile maintaining core size and by increasing the thickness of thecover. The larger, less dense finished ball exhibits lower spin ratesafter club impact than conventional balls.

BACKGROUND OF THE INVENTION

Spin rate is an important golf ball characteristic for both the skilledand unskilled golfer. High spin rates allow for the more skilled golfer,such as PGA professionals and low handicap players, to maximize controlof the golf ball. This is particularly beneficial to the more skilledgolfer when hitting an approach shot to a green. The ability tointentionally produce “back spin”, thereby stopping the ball quickly onthe green, and/or “side spin” to draw or fade the ball, substantiallyimproves the golfer's control over the ball. Thus, the more skilledgolfer generally prefers a golf ball exhibiting high spin rateproperties.

However, a high spin golf ball is not desirous by all golfers,particularly high handicap players who cannot intentionally control thespin of the ball. In this regard, less skilled golfers, have, amongothers, two substantial obstacles to improving their game: slicing andhooking. When a club head meets a ball, an unintentional side spin isoften imparted which sends the ball off its intended course. The sidespin reduces one's control over the ball as well as the distance theball will travel. As a result, unwanted strokes are added to the game.

Consequently, while the more skilled golfer desires a high spin golfball, a more efficient ball for the less skilled player is a golf ballthat exhibits low spin properties. The low spin ball reduces slicing andhooking and enhances roll distance for the amateur golfer.

The present inventors have addressed the need for developing a golf ballhaving a reduced spin rate after club impact, while at the same timemaintaining durability, playability and resiliency characteristicsneeded for repeated use. The reduced spin rate golf ball of the presentinvention meets the rules and regulations established by the UnitedStates Golf Association (U.S.G.A.).

Along these lines, the U.S.G.A. has set forth five (5) specificregulations that a golf ball must conform to. The U.S.G.A. rules requirethat a ball be no smaller than 1.680 inches in diameter. However,notwithstanding this restriction, there is no specific limitation as tothe maximum permissible diameter of a golf ball. As a result, a golfball can be as large as desired so long as it is larger than 1.680inches in diameter and so long as the other four (4) specificregulations are met.

The U.S.G.A. rules also require that balls weigh no more than 1.620ounces, and that their initial velocity may not exceed 250 feet persecond with a maximum tolerance of 2%, or up to 255 ft./sec. Further,the U.S.G.A. rules state that a ball may not travel a distance greaterthan 280 yards with a test tolerance of 6% when hit by the U.S.G.A.outdoor driving machine under specific conditions.

It has been determined by the present inventors that the combination ofa relatively soft core (i.e. Riehle compression of about 0.075 to 0.115)and a hard cover (i.e. Shore D hardness of 65 or more) significantlyreduces the overall spin rate of the resulting two piece golf ball. Theinventors have also learned that an increase in cover thickness, therebyincreasing the overall diameter of the resulting molded golf ball,further reduces spin rate.

Top-grade golf balls sold in the United States may be generallyclassified as one of two types: two-piece or three-piece balls. Thetwo-piece ball, exemplified by the balls sold by Spalding & EvenfloCompanies, Inc. (the assignee of the present invention through itswholly owned subsidiary, Lisco, Inc.) under the trademark TOP-FLITE,consists of a solid polymeric core and a separately formed outer cover.The so-called three-piece balls, exemplified by the balls sold under thetrademark TITLEIST by the Acushnet Company, consist of a liquid (e.g.,TITLEIST TOUR 384) or solid (e.g., TITLEIST DT) center, elastomericthread windings about the center, and a cover.

Spalding's two-piece golf balls are produced by molding a natural(balata) or synthetic (i.e. thermoplastic resin such as an ionomerresin) polymeric cover composition around a preformed polybutadiene(rubber) core. During the molding process, the desired dimple pattern ismolded into the cover material. In order to reduce the number of coatingsteps involved in the finishing of the golf balls, a color pigment ordye and, in many instances, an optical brightener, are added directly tothe generally “off white” colored polymeric cover composition prior tomolding. By incorporating the pigment and/or optical brightener in thecover composition molded onto the golf ball core, this processeliminates the need for a supplemented pigmented painting step in orderto produce a white or colored (notably orange, pink and yellow) golfball.

With respect to multi-layered golf balls, Spalding is the leadingmanufacturer of two-piece golf balls in the world. Spalding manufacturesover sixty (60) different types of two-piece balls which vary distinctlyin such properties as playability (i.e. spin rate, compression, feel,etc.), travel distance (initial velocity, C.O.R., etc.), durability(impact, cut and weather resistance) and appearance (i.e. whiteness,reflectance, yellowness, etc.) depending upon the ball's core, cover andcoating materials, as well as the ball's surface configuration (i.e.dimple pattern). Consequently, Spalding's two-piece golf balls offerboth the amateur and professional golfer a variety of performancecharacteristics to suit an individual's game.

In regard to the specific components of a golf ball, although the natureof the cover can, in certain instances, make a significant contributionto the overall feel, spin (control), coefficient of restitution (C.O.R.)and initial velocity of a ball (see, for example, U.S. Pat. No.3,819,768 to Molitor), the initial velocity of two-piece and three-pieceballs is determined mainly by the coefficient of restitution of thecore. The coefficient of restitution of the core of wound (i.e.three-piece) balls can be controlled within limits by regulating thewinding tension and the thread and center composition. With respect totwo-piece balls, the coefficient of restitution of the core is afunction of the properties of the elastomer composition from which it ismade.

The cover component of a golf ball is particularly influential ineffecting the compression (feel), spin rates (control), distance(C.O.R.), and durability (i.e. impact resistance, etc.) of the resultingball. Various cover compositions have been developed by Spalding andothers in order to optimize the desired properties of the resulting golfballs.

Over the last twenty (20) years, improvements in cover and core materialformulations and changes in dimple patterns have more or lesscontinually improved golf ball distance. Top-grade golf balls, however,must meet several other important design criteria. To successfullycompete in today's golf ball market, a golf ball should be resistant tocutting and must be finished well; it should hold a line in putting andshould have good click and feel. In addition, the ball should exhibitspin and control properties dictated by the skill and experience of theend user.

The present invention is directed to improved top-grade golf ballshaving reduced spin rates. The improved golf balls offer the lessskilled golfer better control over his or her shots and allow forgreater distance.

In an alternative embodiment, the spin rate of the ball is furtherreduced by increasing the thickness of the cover and/or decreasing theweight and softness of the core. By increasing the cover thicknessand/or the overall diameter of the resulting molded golf ball, enhancedreduction in spin rate is observed.

With respect to the increased size of the ball, over the years golf ballmanufacturers have generally produced golf balls at or around theminimum size and maximum weight specifications set forth by the U.S.G.A.There have, however, been exceptions, particularly in connection withthe manufacture of golf balls for teaching aids. For example, oversized,overweight (and thus unauthorized) golf balls have been on sale for useas golf teaching aids (see U.S. Pat. No. 3,201,384 to Barber).

Oversized golf balls are also disclosed in New Zealand Patent 192,618dated Jan. 1, 1980, issued to a predecessor of the present assignee.This patent teaches an oversize golf ball having a diameter between1.700 and 1.730 inches and an oversized core of resilient material (i.e.about 1.585 to 1.595 inches in diameter) so as to increase thecoefficient of restitution.

Additionally, the patent discloses that the ball should include a coverhaving a thickness less than the cover thickness of conventional balls(i.e. a cover thickness of about 0.050 inches as opposed to 0.090 inchesfor conventional two-piece balls).

In addition, it is also noted that golf balls made by Spalding in 1915were of a diameter ranging from 1.630 inches to 1.710 inches. As thediameter of the ball increased, the weight of the ball also increased.These balls were comprised of covers made up of balata/gutta percha andcores made from solid rubber or liquid sacs and wound with elasticthread.

Golf balls known as the LYNX JUMBO were also commercially available byLynx in October, 1979. These balls had a diameter of 1.76 to 1.80inches. It met with little or no commercial success. The LYNX JUMBOballs consisted of a core comprised of wound core and a cover comprisedof natural or synthetic balata.

However, notwithstanding the enhanced diameters of these golf balls,none of these balls produced the enhanced spin reduction characteristicsand overall playability, distance and durability properties of thepresent invention and/or fall within the regulations set forth by theU.S.G.A. An object of the present invention is to produce a U.S.G.A.regulation golf ball having improved low spin properties whilemaintaining the resilience and durability characteristics necessary forrepetitive play.

These and other objects and features of the invention will be apparentfrom the following summary and description of the invention and from theclaims.

SUMMARY OF THE INVENTION

The present invention is directed to improved golf balls having a lowrate of spin upon club impact. The golf balls comprise a softpolybutadiene core and a hard cover. The hard cover is preferably sizedto be larger than conventional diameters. The low spin rate enables theball to travel a greater distance. In addition, the low spin rateprovides the less skilled golfer with more control. This is because thelow spin rate decreases undesirable side spin which leads to slicing andhooking. The combination of a hard cover and a soft core provides for aball having a lower than anticipated spin rate while maintaining highresilience and good durability.

The golf ball comprises a core and a cover. The core has a Riehlecompression of at least 0.075, preferably 0.075 to about 0.115, and aPGA compression of about 45 to 85. The cover has a Shore D hardness ofat least 65.

In an alternative embodiment, the resulting ball is larger than thestandard 1.680 inch golf ball. Its diameter is in the range of about1.680 to 1.800 inches, more likely in the range of about 1.700 to 1.800inches, preferably in the range of 1.710-1.730 inches, and mostpreferably in the range of about 1.717-1.720 inches. The larger diameterof the golf ball (see FIG. 1) results from the cover thickness whichranges from more than the standard 0.0675 inches up to about 0.130,preferably from about 0.0675 to about 0.1275 inches, more preferably inthe range of about 0.0825 to 0.0925, and most preferably in the range ofabout 0.0860 to 0.0890 inches. The core is of a standard size, roughlyabout 1.540 to 1.545 inches.

The core used in the present invention is a specially produced softenedpolybutadiene elastomeric solid core having a conventional diameter ofabout 1.540 to 1.545 inches. The core is produced from a compositioncomprising a base elastomer selected from polybutadiene and mixtures ofpolybutadiene with other elastomers, at least one metallic salt of anunsaturated carboxylic acid (a co-crosslinking agent), and free radicalinitiator (a co-crosslinking agent). In addition, a suitable andcompatible modifying ingredient including, but not limited to metalactivators, fatty acids, fillers, polypropylene powder and otheradditives may be included.

Of particular concern, only a limited amount of the metallic salt of anunsaturated carboxylic acid is included in the core compositions inorder to produce the degree of core softness and weight desired. In thisregard, it is understood that when a larger overall ball is desired, thecomposition of the core is adjusted so that the molded finished ballfalls within the weight parameters set forth by the U.S.G.A. Since thefinished golf balls must still meet the U.S.G.A. weight limitation of1.620 ounces, the core component of the larger and thicker covered ballsare designed to be not only softer, but also lighter in weight.

In such circumstances, the specific gravity of the core is less thanthat of a standard core since the larger ball must weigh the same as astandard ball. The core generally weighs about 36 to 37 grams for anstandard sized finished ball and about 33 to 34 grams for an oversizedfinished ball.

The core composition produces a softer molded core which still maintainsthe resilience (C.O.R.), compression (hardness) and durabilitycharacteristics required. The overall molded core has a PGA compressionof about 45 to 85, preferably in the range of about 70-80. Its Riehlecompression is about 0.075 or more, preferably in the range of 0.075 to0.115, and the resilience of the core is about 0.760 to 0.780.

The cover is preferably comprised of a hard, high-stiffness ionomerresin, most preferably a metal cation neutralized high acid ionomerresin containing more than 16% carboxylic acid by weight, or blendthereof. The cover has a Shore D hardness of about 65 or greater.

With respect to the ionomeric cover composition of the is invention,ionomeric resins are polymers containing interchain ionic bonding. As aresult of their toughness, durability, and flight characteristics,various ionomeric resins sold by E.I. DuPont de Nemours & Company underthe trademark “Surlyn®” and more recently, by the Exxon Corporation (seeU.S. Pat. No. 4,911,451) under the trademark “Escor®” and the tradename“Iotek”, have become the materials of choice for the construction ofgolf ball covers over the traditional “balata” (trans-polyisoprene,natural or synthetic) rubbers.

Ionomeric resins are generally ionic copolymers of an olefin, such asethylene, and a metal salt of an unsaturated carboxylic acid, such asacrylic acid, methacrylic acid or maleic acid. In some instances, anadditional softening comonomer such as an acrylate can also be includedto form a terpolymer. The pendent ionic groups in the ionomeric resinsinteract to form ion-rich aggregates contained in a non-polar polymermatrix. The metal ions, such as sodium, zinc, magnesium, lithium,potassium, calcium, etc. are used to neutralize some portion of the acidgroups in the copolymer resulting in a thermoplastic elastomerexhibiting enhanced properties, i.e., improved durability, etc. for golfball construction over balata.

The ionomeric resins utilized to produce cover compositions can beformulated according to known procedures such as those set forth in U.S.Pat. No. 3,421,766 or British Patent No. 963,380, with neutralizationeffected according to procedures disclosed in Canadian Patent Nos.674,595 and 713,631, wherein the ionomer is produced by copolymerizingthe olefin and carboxylic acid to produce a copolymer having the acidunits randomly distributed along the polymer chain. Broadly, the ioniccopolymer generally comprises one or more α-olefins and from about 9 toabout 20 weight percent of α, β-ethylenically unsaturated mono- ordicarboxylic acid, the basic copolymer neutralized with metal ions tothe extent desired.

At least about 20% of the carboxylic acid groups of the copolymer areneutralized by the metal ions (such as sodium, potassium, zinc, calcium,magnesium, and the like) and exist in the ionic state. Suitable olefinsfor use in preparing the ionomeric resins include ethylene, propylene,butene-1, hexene-1 and the like. Unsaturated carboxylic acids includeacrylic, methacrylic, ethacrylic, α-chloroacrylic, crotonic, maleic,fumaric, itaconic acids, and the like. The ionomeric resins utilized inthe golf ball industry are generally copolymers of ethylene with acrylic(i.e., Escor®) and/or methacrylic (i.e., Surlyn®) acid. In addition, twoor more types of ionomeric resins may be blended in to the covercompositions in order to produce the desired properties of the resultinggolf balls.

The cover compositions which may be used in making the golf balls of thepresent invention are set forth in detail but not limited to those incopending U.S. Ser. No. 07/776,803 filed Oct. 15, 1991, and Ser. No.07/901,660 filed Jun. 19, 1992, both incorporated herein by reference.In short, the cover material is comprised of hard, high stiffnessionomer resins, preferably containing relatively high amounts of acid(i.e., greater than 16 weight percent acid, preferably from about 17 toabout 25 weight percent acid, and more preferably from about 18.5 toabout 21.5 weight percent) and at least partially neutralized with metalions (such as sodium, zinc, potassium, calcium, magnesium and the like).The high acid resins are blended and melt processed to producecompositions exhibiting enhanced hardness and coefficient of restitutionvalues when compared to low acid ionomers, or blends of low acid ionomerresins containing 16 weight percent acid or less.

The preferred cover compositions are made from specific blends of two ormore high acid ionomers with other cover additives which do not exhibitthe processing, playability, distance and/or durability limitationsdemonstrated by the prior art. However, as more particularly indicatedbelow, the cover composition can also be comprised of one or more lowacid ionomers so long as the molded covers exhibit a hardness of 65 ormore on the Shore D scale.

Through the use of the softer cores and the hard cover, is overallfinished balls of the invention exhibit significantly lower spin ratesthan conventional balls of equal size and weight.

Further, reduction in spin are also produced by increasing the thicknessof the cover and by decreasing the weight of the softened core.

Further scope of the applicability of the present invention will becomeapparent from the detailed description given hereinafter. It should,however, be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings which are presentedfor the purposes of illustrating the invention and not for purposes oflimiting the same.

FIG. 1 illustrates a partially broken-away view of the improved golfball of the present invention wherein D is the diameter of the ball; Cis the diameter of the core and T is the thickness of the cover.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the development of a golf ball having alow spin rate as a result of combining a relatively soft core and a hardcover. Such a lower spin rate after club impact contributes tostraighter shots when the ball is mis-hit, greater efficiency in flight,and a lesser degree of energy loss on impact with the ground, addingincreased roll or distance. In addition, by increasing the diameter ofthe overall ball of the present invention beyond the U.S.G.A. minimum of1.680 inches, the spin rate is still further decreased by up to around500 r.p.m. or more upon being hit with a No. 9 iron travelling at aspeed of 105 feet per second (fps). In this embodiment of the invention,the ball, even though of larger diameter, uses substantially the samesize core as a standard golf ball, the difference in size is provided bythe additional thickness in the cover of the ball. This larger, low spinball produces even greater control and flight efficiency than thestandard size ball embodiment of the present invention.

Notwithstanding the overall size differences of the various embodimentsof the present invention, the core of the present invention isrelatively soft and of similar size. It has a Riehle compression ofabout 0.075 or more, preferably about 0.075 to about 0.115, and arelatively low PGA compression of about 40 to 85, preferably about70-80.

The specially produced core compositions and resulting molded cores ofthe present invention are manufactured using relatively conventionaltechniques. In this regard, the core compositions of the invention maybe based on polybutadiene, and mixtures of polybutadiene with otherelastomers. It is preferred that the base elastomer have a relativelyhigh molecular weight. The broad range for the molecular weight ofsuitable base elastomers is from about 50,000 to about 500,000. A morepreferred range for the molecular weight of the base elastomer is fromabout 100,000 to about 500,000. As a base elastomer for the corecomposition, cis-polybutadiene is preferably employed, or a blend ofcis-polybutadiene with other elastomers may also be utilized. Mostpreferably, cis-polybutadiene having a weight-average molecular weightof from about 100,000 to about 500,000 is employed. Along this line, ithas been found that the high cis-polybutadiene manufactured and sold byShell Chemical Co., Houston, Tex., under the tradename Cariflex BR-1220,and the polyisoprene available from Muehlstein, H & Co., Greenwich,Conn. under the designation “SKI 35” are particularly well suited.

The unsaturated carboxylic acid component of the core composition (aco-crosslinking agent) is the reaction product of the selectedcarboxylic acid or acids and an oxide or carbonate of a metal such aszinc, magnesium, barium, calcium, lithium, sodium, potassium, cadmium,lead, tin, and the like. Preferably, the oxides of polyvalent metalssuch as zinc, magnesium and cadmium are used, and most preferably, theoxide is zinc oxide.

Exemplary of the unsaturated carboxylic acids which find utility in thepresent core compositions are acrylic acid, methacrylic acid, itaconicacid, crotonic acid, sorbic acid, and the like, and mixtures thereof.Preferably, the acid component is either acrylic or methacrylic acid.Usually, from about 15 to about 25, and preferably from about 17 toabout 21 parts by weight of the carboxylic acid salt, such as zincdiacrylate, is included in the core composition. The unsaturatedcarboxylic acids and metal salts thereof are generally soluble in theelastomeric base, or are readily dispersible.

The free radical initiator included in the core composition is any knownpolymerization initiator (a co-crosslinking agent) which decomposesduring the cure cycle. The term “free radical initiator” as used hereinrefers to a chemical which, when added to a mixture of the elastomericblend and a metal salt of an unsaturated, carboxylic acid, promotescrosslinking of the elastomers by the metal salt of the unsaturatedcarboxylic acid. The amount of the selected initiator present isdictated only by the requirements of catalytic activity as apolymerization initiator. Suitable initiators include peroxides,persulfates, azo compounds and hydrazides. Peroxides which are readilycommercially available are conveniently used in the present invention,generally in amounts of from about 0.1 to about 10.0 and preferably inamounts of from about 0.3 to about 3.0 parts by weight per each 100parts of elastomer.

Exemplary of suitable peroxides for the purposes of the presentinvention are dicumyl peroxide, n-butyl 4,4′-bis (butylperoxy) valerate,1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, di-t-butyl peroxideand 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane and the like, as well asmixtures thereof. It will be understood that the total amount ofinitiators used will vary depending on the specific end product desiredand the particular initiators employed.

Examples of such commercially available peroxides are Luperco 230 or 231XL sold by Atochem, Lucidol Division, Buffalo, N.Y., and Trigonox 17/40or 29/40 sold by Akzo Chemie America, Chicago, Ill. In this regardLuperco 230 XL and Trigonox 17/40 are comprised of n-butyl 4,4-bis(butylperoxy) valerate; and, Luperco 231 XL and Trigonox 29/40 arecomprised of 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane. The onehour half life of Luperco 231 XL is about 112° C., and the one hour halflife of Trigonox 29/40 is about 129° C.

The core compositions of the present invention may additionally containany other suitable and compatible modifying ingredients including, butnot limited to, metal oxides, fatty acids, and diisocyanates andpolypropylene powder resin. For example, Papi 94, a polymericdiisocyanate, commonly available from Dow Chemical Co., Midland, Mich.,is an optional component in the rubber compositions. It can range fromabout 0 to 5 parts by weight per 100 parts by weight rubber (phr)component, and acts as a moisture scavenger. In addition, it has beenfound that the addition of a polypropylene powder resin results in acore which is too hard (i.e. exhibits low compression) and thus allowsfor a reduction in the amount of crosslinking agent utilized to softenthe core to a normal or below normal compression.

Furthermore, because polypropylene powder resin can be added to corecomposition without an increase in weight of the molded core uponcuring, the addition of the polypropylene powder allows for the additionof higher specific gravity fillers, such as mineral fillers. Since thecrosslinking agents utilized in the polybutadiene core compositions areexpensive and/or the higher specific gravity fillers are relativelyinexpensive, the addition of the polypropylene powder resinsubstantially lowers the cost of the golf ball cores while maintaining,or lowering, weight and compression.

The polypropylene (C₃H₅) powder suitable for use in the presentinvention has a specific gravity of about 0.90 g/cm³, a melt flow rateof about 4 to about 12 and a particle size distribution of greater than99% through a 20 mesh screen. Examples of such polypropylene powderresins include those sold by the Amoco Chemical Co., Chicago, Ill.,under the designations “6400 P”, “7000 P” and “7200 P”. Generally, from0 to about 25 parts by weight polypropylene powder per each 100 parts ofelastomer are included in the present invention.

Various activators may also be included in the compositions of thepresent invention. For example, zinc oxide and/or magnesium oxide areactivators for the polybutadiene. The activator can range from about 2to about 30 parts by weight per 100 parts by weight of the rubbers (phr)component.

Moreover, filler-reinforcement agents may be added to the composition ofthe present invention. Since the specific gravity of polypropylenepowder is very low, and when compounded, the polypropylene powderproduces a lighter molded core, when polypropylene is incorporated inthe core compositions, relatively large amounts of higher gravityfillers may be added so long as the specific core weight limitations aremet. Additional benefits may be obtained by the incorporation ofrelatively large amounts of higher specific gravity, inexpensive mineralfillers such as calcium carbonate. Such fillers as are incorporated intothe core compositions should be in finely divided form, as for example,in a size generally less than about 30 mesh and preferably less thanabout 100 mesh U.S. standard size. The amount of additional fillerincluded in the core composition is primarily dictated by weightrestrictions and preferably is included in amounts of from about 10 toabout 100 parts by weight per 100 parts rubber.

The preferred fillers are relatively inexpensive and heavy and serve tolower the cost of the ball and to increase the weight of the ball toclosely approach the U.S.G.A. weight limit of 1.620 ounces. However, ifthicker cover compositions are to be applied to the core to producelarger than normal (i.e. greater than 1.680 inches in diameter) balls,use of such fillers and modifying agents will be limited in order tomeet the U.S.G.A. maximum weight limitations of 1.620 ounces. Exemplaryfillers include mineral fillers such as limestone, silica, micabarytes,calcium carbonate, or clays. Limestone is ground calcium/magnesiumcarbonate and is used because it is an inexpensive, heavy filler.

As indicated, ground flash filler may be incorporated and is preferably20 mesh ground up center stock from the excess flash from compressionmolding. It lowers the cost and may increase the hardness of the ball.

Fatty acids or metallic salts of fatty acids may also be included in thecompositions, functioning to improve moldability and processing.Generally, free fatty acids having from about 10 to about 40 carbonatoms, and preferably having from about 15 to about 20 carbon atoms, areused. Exemplary of suitable fatty acids are stearic acid and linoleicacids, as well as mixtures thereof. Exemplary of suitable metallic saltsof fatty acids include zinc stearate. When included in the corecompositions, the fatty acid component is present in amounts of fromabout 1 to about 25, preferably in amounts from about 2 to about 15parts by weight based on 100 parts rubber (elastomer).

It is preferred that the core compositions include stearic acid as thefatty acid adjunct in an amount of from about 2 to about 5 parts byweight per 100 parts of rubber.

Diisocyanates may also be optionally included in the core compositionswhen utilized, the diioscyanates are included in amounts of from about0.2 to about 5.0 parts by weight based on 100 parts rubber. Exemplary ofsuitable diisocyanates is 4,4′-diphenylmethane diisocyanate and otherpolyfunctional isocyanates know to the art.

Furthermore, the dialkyl tin difatty acids set forth in U.S. Pat. No.4,844,471, the dispersing agents disclosed in U.S. Pat. No. 4,838,556,and the dithiocarbamates set forth in U.S. Pat. No. 4,852,884 may alsobe incorporated into the polybutadiene compositions of the presentinvention. The specific types and amounts of such additives are setforth in the above identified patents, which are incorporated herein byreference.

The core compositions of the invention are generally comprised of 100parts by weight of a base elastomer (or rubber) selected frompolybutadiene and mixtures of polybutadiene with other elastomers, 15 to25 parts by weight of at least one metallic salt of an unsaturatedcarboxylic acid, and 1 to 10 parts by weight of a free radicalinitiator.

As indicated above, additional suitable and compatible modifying agentssuch as particulate polypropylene resin, fatty acids, and secondaryadditives such as Pecan shell flour, ground flash (i.e. grindings frompreviously manufactured cores of substantially identical construction),barium sulfate, zinc oxide, etc. may be added to the core compositionsto adjust the weight of the ball as necessary in order to have thefinished molded ball (core, cover and coatings) to closely approach theU.S.G.A. weight limit of 1.620 ounces.

In producing golf ball cores utilizing the present compositions, theingredients may be intimately mixed using, for example, two roll millsor a Banbury mixer until the composition is uniform, usually over aperiod of from about 5 to about 20 minutes. The sequence of addition ofcomponents is not critical. A preferred blending sequence is as follows.

The elastomer, polypropylene powder resin (if desired), fillers, zincsalt, metal oxide, fatty acid, and the metallic dithiocarbamate (ifdesired), surfactant (if desired), and tin difatty acid (if desired),are blended for about 7 minutes in an internal mixer such as a Banburymixer. As a result of shear during mixing, the temperature rises toabout 200° F. The initiator and diisocyanate are then added and themixing continued until the temperature reaches about 220° F. whereuponthe batch is discharged onto a two roll mill, mixed for about one minuteand sheeted out.

The sheet is rolled into a “pig” and then placed in a Barwell preformerand slugs are produced. The slugs are then subjected to compressionmolding at about 320° F. for about 14 minutes. After molding, the moldedcores are cooled, the cooling effected at room temperature for about 4hours or in cold water for about one hour. The molded cores aresubjected to a centerless grinding operation whereby a thin layer of themolded core is removed to produce a round core having a diameter of1.540 to 1.545 inches. Alternatively, the cores are used in theas-molded state with no grinding needed to achieve roundness.

The mixing is desirably conducted in such a manner that the compositiondoes not reach incipient polymerization temperatures during the blendingof the various components.

Usually the curable component of the composition will be cured byheating the composition at elevated temperatures on the order of fromabout 275° F. to about 350° F., preferably and usually from about 290°F. to about 325° F., with molding of the composition effectedsimultaneously with the curing thereof. The composition can be formedinto a core structure by any one of a variety of molding techniques,e.g. injection, compression, or transfer molding. When the compositionis cured by heating, the time required for heating will normally beshort, generally from about 10 to about 20 minutes, depending upon theparticular curing agent used. Those of ordinary skill in the artrelating to free radical curing agents for polymers are conversant withadjustments of cure times and temperatures required to effect optimumresults with any specific free radical agent.

After molding, the core is removed from the mold and the surfacethereof, preferably treated to facilitate adhesion thereof to thecovering materials. Surface treatment can be effected by any of theseveral techniques known in the art, such as corona discharge, ozonetreatment, sand blasting, and the like. Preferably, surface treatment iseffected by grinding with an abrasive wheel.

The core is converted into a golf ball by providing at least one layerof covering material thereon, ranging in thickness from about 0.070 toabout 0.130 inches and preferably from about 0.0675 to about 0.1275inches.

The cover has a Shore D hardness of 65 or greater. Its compositionincludes a hard, high stiffness preferably high acid ionomer such asthat sold by E.I. DuPont de Nemours & Company under the trademark“Surlyn®” and by Exxon Corporation under the trademark “Escor®” ortradename “Iotek”, or blends thereof. In addition to the Surlyn® andEscor® or Iotek ionomers, the cover may comprise any ionomer whicheither alone or in combination with other ionomers produces a moldedcover having a Shore D hardness of at least 65. These include lithiumionomers or blends of ionomers with harder non-ionic polymers such asnylon, polyphenylene oxide and other compatible thermoplastics. Asbriefly mentioned above, examples of cover compositions which may beused are set forth in detail in copending U.S. Ser. No. 07/776,803 filedOct. 15, 1991, and Ser. No. 07/901,660 filed Jun. 19, 1992, bothincorporated herein by reference. Of course, the cover compositions arenot limited in any way to those compositions set forth in said copendingapplications.

The high acid ionomers suitable for use in the present invention areionic copolymers which are the metal, i.e., sodium, zinc, magnesium,etc., salts of the reaction product of an olefin having from about 2 to8 carbon atoms and an unsaturated monocarboxylic acid having from about3 to 8 carbon atoms. Preferably, the ionomeric resins are copolymers ofethylene and either acrylic or methacrylic acid. In some circumstances,an additional comonomer such as an acrylate ester (i.e., iso- orn-butylacrylate, etc.) can also be included to produce a softerterpolymer. The carboxylic acid groups of the copolymer are partiallyneutralized (i.e., approximately 10-75%, preferably 30-70%) by the metalions. Each of the high acid ionomer resins included in the covercompositions of the invention contains greater than about 16% by weightof a carboxylic acid, preferably from about 17% to about 25% by weightof a carboxylic acid, more preferably from about 18.5% to about 21.5% byweight of a carboxylic acid.

Although the cover composition preferably includes a high acid ionomericresin and the scope of the patent embraces all known high acid ionomericresins falling within the parameters set forth above, only a relativelylimited number of these high acid ionomeric resins are currentlyavailable. In this regard, the high acid ionomeric resins available fromE.I. DuPont de Nemours Company under the trademark “Surlyn®”, and thehigh acid ionomer resins available from Exxon Corporation under thetrademark “Escor®” or tradename “Iotek” are examples of available highacid ionomeric resins which may be utilized in the present invention.

The high acid ionomeric resins available from Exxon under thedesignation “Escor®” and or “Iotek”, are somewhat similar to the highacid ionomeric resins available under the “Surlyn®” trademark. However,since the Escor®/Iotek ionomeric resins are sodium or zinc salts ofpoly(ethylene acrylic acid) and the “Surlyn®” resins are zinc, sodium,magnesium, etc. salts of poly(ethylene methacrylic acid), distinctdifferences in properties exist.

Examples of the high acid methacrylic acid based ionomers found suitablefor use in accordance with this invention include Surlyn® AD-8422(sodium cation), Surlyn® 8162 (zinc cation), Surlyn® SEP-503-1 (zinccation), and Surlyn® SEP-503-2 (magnesium cation). According to DuPont,all of these ionomers contain from about 18.5 to about 21.5% by weightmethacrylic acid.

More particularly, Surlyn® AD-8422 is currently commercially availablefrom DuPont in a number of different grades (i.e., AD-8422-2, AD-8422-3,AD-8422-5, etc.) based upon differences in melt index. According toDuPont, Surlyn® AD-8422 offers the following general properties whencompared to Surlyn® 8920 the stiffest, hardest of all on the low acidgrades (referred to as “hard” ionomers in U.S. Pat. No. 4,884,814):

LOW ACID HIGH ACID (15 wt % Acid) (>20 wt % Acid) SURLYN ® SURLYN ®SURLYN ® 8920 8422-2 8422-3 IONOMER Cation Na Na Na Melt Index 1.2 2.81.0 Sodium, Wt % 2.3 1.9 2.4 Base Resin MI 60 60 60 MP¹, ° C. 88 86 85FP, ° C. 47 48.5 45 COMPRESSION MOLDING² Tensile Break, 4350 4190 5330psi Yield, psi 2880 3670 3590 Elongation, % 315 263 289 Flex Mod, 53.276.4 88.3 K psi Shore D 66 67 68 hardness ¹DSC second heat, 10° C./minheating rate. ²Samples compression molded at 150° C. annealed 24 hoursat 60° C. 8422-2 -3 were homogenized at 190° C. before molding.

In comparing Surlyn® 8920 to Surlyn® 8422-2 and Surlyn® 8422-3, it isnoted that the high acid Surlyn® 8422-2 and 8422-3 ionomers have ahigher tensile yield, lower elongation, slightly higher Shore D hardnessand much higher flexural modulus. Surlyn® 8920 contains 15 weightpercent methacrylic acid and is 59% neutralized with sodium.

In addition, Surlyn® SEP-503-1 (zinc cation) and Surlyn® SEP-503-2(magnesium cation) are high acid zinc and magnesium versions of theSurlyn® AD 8422 high acid ionomers. When compared to the Surlyn® AD 8422high acid ionomers, the Surlyn SEP-503-1 and SEP-503-2 ionomers can bedefined as follows:

Surlyn ® Ionomer Ion Melt Index Neutralization % AD 8422-3 Na 1.0 45 SEP503-1 Zn 0.8 38 SEP 503-2 Mg 1.8 43

Furthermore, Surlyn® 8162 is a zinc cation ionomer resin containingapproximately 20% by weight (i.e. 18.5-21.5% weight) methacrylic acidcopolymer that has been 30-70% neutralized. Surlyn® 8162 is currentlycommercially available from DuPont.

Examples of the high acid acrylic acid based ionomers suitable for usein the present invention include the Escor® or Iotek high acid ethyleneacrylic acid ionomers produced by Exxon. In this regard, Escor® or Iotek959 is a sodium ion neutralized ethylene-acrylic acid copolymer.According to Exxon, Ioteks 959 and 960 contain from about 19.0 to about21.0% by weight acrylic acid with approximately 30 to about 70 percentof the acid groups neutralized with sodium and zinc ions, respectively.The physical properties of these high acid acrylic acid based ionomersare as follows:

ESCOR ® ESCOR ® PROPERTY (IOTEK) 959 (IOTEK) 960 Melt Index, g/10 min2.0 1.8 Cation Sodium Zinc Melting Point, ° F. 172 174 Vicat SofteningPoint, ° F. 130 131 Tensile @ Break, psi 4600 3500 Elongation @ Break, %325 430 Hardness, Shore D 66 57 Flexural Modulus, psi 66,000 27,000

Furthermore, as a result of the development by the inventors of a numberof new high acid ionomers neutralized to various extents by severaldifferent types of metal cations, such as by manganese, lithium,potassium, calcium and nickel cations, several new high acid ionomersand/or high acid ionomer blends besides sodium, zinc and magnesium highacid ionomers or ionomer blends are now available for golf ball coverproduction. It has been found that these new cation neutralized highacid ionomer blends produce cover compositions exhibiting enhancedhardness and resilience due to synergies which occur during processing.

Consequently, the metal cation neutralized high acid ionomer resinsrecently produced can be blended to produce substantially harder coveredgolf balls having higher C.O.R.'s than those produced by the low acidionomer covers presently commercially available.

More particularly, several new metal cation neutralized high acidionomer resins have been produced by the inventors by neutralizing, tovarious extents, high acid copolymers of an alpha-olefin and an alpha,beta-unsaturated carboxylic acid with a wide variety of different metalcation salts. This discovery is the subject matter of U.S. applicationSer. No. 901,680, incorporated herein by reference. It has been foundthat numerous new metal cation neutralized high acid ionomer resins canbe obtained by reacting a high acid copolymer (i.e. a copolymercontaining greater than 16% by weight acid, preferably from about 17 toabout 25 weight percent acid, and more preferably about 20 weightpercent acid), with a metal cation salt capable of ionizing orneutralizing the copolymer to the extent desired (i.e. from about 10% to90%).

The base copolymer is made up of greater than 16% by weight of an alpha,beta-unsaturated carboxylic acid and an alpha-olefin. Optionally, asoftening comonomer can be included in the copolymer. Generally, thealpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene,and the unsaturated carboxylic acid is a carboxylic acid having fromabout 3 to 8 carbons.

Examples of such acids include acrylic acid, methacrylic acid,ethacrylic acid, chloroacrylic acid, crotonic acid, maleic acid, fumaricacid, and itaconic acid, with acrylic acid being preferred.

The softening comonomer that can be optionally included in the inventionmay be selected from the group consisting of vinyl esters of aliphaticcarboxylic acids wherein the acids have 2 to 10 carbon atoms, vinylethers wherein the alkyl groups contains 1 to 10 carbon atoms, and alkylacrylates or methacrylates wherein the alkyl group contains 1 to 10carbon atoms. Suitable softening comonomers include vinyl acetate,methyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, butyl acrylate, butyl methacrylate, or the like.

Consequently, examples of a number of copolymers suitable for use toproduce the high acid ionomers included in the present inventioninclude, but are not limited to, high acid embodiments of anethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer,an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer,an ethylene/methacrylic acid/vinyl acetate copolymer, anethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymerbroadly contains greater than 16% by weight unsaturated carboxylic acid,from about 30 to about 83% by weight ethylene and from 0 to about 40% byweight of a softening comonomer. Preferably, the copolymer containsabout 20% by weight unsaturated carboxylic acid and about 80% by weightethylene. Most preferably, the copolymer contains about 20% acrylic acidwith the remainder being ethylene.

Along these lines, examples of the preferred high acid base copolymerswhich fulfill the criteria set forth above, are a series ofethylene-acrylic copolymers which are commercially available from TheDow Chemical Company, Midland, Mich., under the “Primacor” designation.These high acid base copolymers exhibit the typical properties set forthbelow in Table 1.

TABLE 1 Typical Properties of Primacor Ethylene-Acrylic Acid CopolymersMELT TENSILE FLEXURAL VICAT PERCENT DENSITY, INDEX, YD. ST MODULUS SOFTPT SHORE D GRADE ACID glcc g/10 min (psi) (psi) (° C.) HARDNESS ASTMD-792 D-1238 D-638 D-790 D-1525 D-2240 5980 20.0 0.958 300.0 — 4800 4350 5990 20.0 0.955 1300.0 650 2600 40 42 5990 20.0 0.955 1300.0 650 320040 42 5981 20.0 0.960 300.0 900 3200 46 48 5981 20.0 0.960 300.0 9003200 46 48 5983 20.0 0.958 500.0 850 3100 44 45 5991 20.0 0.953 2600.0635 2600 38 40 ¹The Melt Index values are obtained according to ASTMD-1238, at 190° C..

Due to the high molecular weight of the Primacor 5981 grade of theethylene-acrylic acid copolymer, this copolymer is the more preferredgrade utilized in the invention.

The metal cation salts utilized in the invention are those salts whichprovide the metal cations capable of neutralizing, to various extents,the carboxylic acid groups of the high acid copolymer. These includeacetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium,potassium, nickel, magnesium, and manganese.

Examples of such lithium ion sources are lithium hydroxide monohydrate,lithium hydroxide, lithium oxide and lithium acetate. Sources for thecalcium ion include calcium hydroxide, calcium acetate and calciumoxide. Suitable zinc ion sources are zinc acetate dihydrate and zincacetate, a blend of zinc oxide and acetic acid. Examples of sodium ionsources are sodium hydroxide and sodium acetate. Sources for thepotassium ion include potassium hydroxide and potassium acetate.Suitable nickel ion sources are nickel acetate, nickel oxide and nickelhydroxide. Sources of magnesium include magnesium oxide, magnesiumhydroxide, magnesium acetate. Sources of manganese include manganeseacetate and manganese oxide.

The new metal cation neutralized high acid ionomer resins are producedby reacting the high acid base copolymer with various amounts of themetal cation salts above the crystalline melting point of the copolymer,such as at a temperature from about 200° F. to about 500° F., preferablyfrom about 250° F. to about 350° F. under high shear conditions at apressure of from about 10 psi to 10,000 psi. Other well known blendingtechniques may also be used. The amount of metal cation salt utilized toproduce the new metal cation neutralized high acid based ionomer resinsis the quantity which provides a sufficient amount of the metal cationsto neutralize the desired percentage of the carboxylic acid groups inthe high acid copolymer. The extent of neutralization is generally fromabout 10% to about 90%.

As indicated below in Table 2, more specifically in Example 1 in U.S.application Ser. No. 901,680, a number of new types of metal cationneutralized high acid ionomers can be obtained from the above indicatedprocess. These include new high acid ionomer resins neutralized tovarious extents with manganese, lithium, potassium, calcium and nickelcations. In addition, when a high acid ethylene/acrylic acid copolymeris utilized as the base copolymer component of the invention and thiscomponent is subsequently neutralized to various extents with the metalcation salts producing acrylic acid based high acid ionomer resinsneutralized with cations such as sodium, potassium, lithium, zinc,magnesium, manganese, calcium and nickel, several new cation neutralizedacrylic acid based high acid ionomer resins are produced.

TABLE 2 Formulation Wt.-% Wt-% Melt Shore D No. Cation SaltNeutralization Index C.O.R. Hardness  1(NaOH)  6.98 67.5 0.9 .804 71 2(NaOH)  5.66 54.0 2.4 .808 73  3(NaOH)  3.84 35.9 12.2  .812 69 4(NaOH)  2.91 27.0 17.5  .812 (brittle)  5(MnAc) 19.6  71.7 7.5 .809 73 6(MnAc) 23.1  88.3 3.5 .814 77  7(MnAc) 15.3  53.0 1.5 .810 72  8(MnAc)26.5  106   0.7 .813 (brittle)  9(LiOH)  4.54 71.3 0.6 .810 74 10(LiOH) 3.38 52.5 4.2 .818 72 11(LiOH)  2.34 35.9 18.6  .815 72 12(KOH)  5.3036.0 19.3  Broke 70 13(KOH)  8.26 57.9  7.18 .804 70 14(KOH) 10.7  77.04.3 .801 67 15(ZnAc) 17.9  71.5 0.2 .806 71 16(ZnAc) 13.9  53.0 0.9 .79769 17(ZnAc)  9.91 36.1 3.4 .793 67 18(MgAc) 17.4  70.7 2.8 .814 7419(MgAc) 20.6  87.1 1.5 .815 76 20(MgAc) 13.8  53.8 4.1 .814 74 21(CaAc)13.2  69.2 1.1 .813 74 22(CaAc)  7.12 34.9 10.1  .808 70 23(MgO)  2.9153.5 2.5 .813 24(MgO)  3.85 71.5 2.8 .808 25(MgO)  4.76 89.3 1.1 .80926(MgO)  1.96 35.7 7.5 .815 27(NiAc) 13.04 61.1 0.2 .802 71 28(NiAc)10.71 48.9 0.5 .799 72 29(NiAc)  8.26 36.7 1.8 .796 69 30(NiAc)  5.6624.4 7.5 .786 64 Controls: 50/50 Blend of Ioteks 8000/7030 C.O.R. =.810/65 Shore D Hardness DuPont High Acid Surlyn ® 8422 (Na) C.O.R. =.811/70 Shore D Hardness DuPont High Acid Surlyn ® 8162 (Zn) C.O.R. =.807/865 Shore D Hardness Exxon High Acid Iotek EX-960 (Zn) C.O.R. =.796/65 Shore D Hardness Control for Formulations 23-26 is 50/50 Iotek8000/7030, C.O.R. = .814, Formulation 26 C.O.R. was normalized to thatcontrol accordingly Control for Formulation Nos. 27-30 is 50/50 Iotek8000/7030, C.O.R. = .807

When compared to low acid versions of similar cation neutralized ionomerresins, the new metal cation neutralized high acid ionomer resinsexhibit enhanced hardness, modulus and resilience characteristics. Theseare properties that are particularly desirable in a number ofthermoplastic fields, including the field golf ball manufacturing.

When utilized in golf ball cover construction, it has been found thatthe new acrylic acid based high acid ionomers extend the range ofhardness beyond that previously obtainable while maintaining thebeneficial properties (i.e. durability, click, feel, etc.) of the softerlow acid ionomer covered balls, such as balls produced utilizing the lowacid ionomers disclosed in U.S. Pat. Nos. 4,884,814 and 4,911,451, andthe recently produced high acid blends disclosed in U.S. applicationSer. No. 776,803.

Moreover, as a result of the development of a number of new acrylic acidbased high acid ionomer resins neutralized to various extents by severaldifferent types of metal cations, such as manganese, lithium, potassium,calcium and nickel cations, several new ionomers or ionomer blends arenow available for golf ball production. By using these high acid ionomerresins harder, stiffer golf balls having higher C.O.R.s, and thus longerdistance, can be obtained.

As will be further noted in the Examples below, other ionomer resins maybe used in the cover compositions, such as low acid ionomer resins, solong as the molded cover produces a Shore D hardness of 65 or more.Properties of some of these low acid ionomer resins are provided in thefollowing table:

Typical Properties of Low Acid Escor ® (Iotek) Ionomers ASTM MethodUnits 4000 4010 8000 8020 Resin Properties Cation type zinc zinc sodiumsodium Melt index D-1238 g/10 min. 2.5 1.5 0.8 1.6 Density D-1505 kg/m³963 963 954 960 Melting Point D-3417 ° C. 90 90 90 87.5 CrystallizationD-3417 ° C. 62 64 56 53 Point Vicat Softening D-1525 ° C. 62 63 61 64Point % Weight 16 — 11 — Acrylic Acid % of Acid 30 — 40 — Groups CationNeutralized Plaque Properties (3 mm thick, compression molded) Tensileat D-638 MPa 24 26 36 31.5 Break Yield point D-638 MPa none none 21 21Elongation at D-638 % 395 420 350 410 break 1% Secant D-638 MPa 160 160300 350 modulus Shore D-2240 — 55 55 61 58 Hardness D 8030 7010 70207030 Resin Properties Cation type sodium zinc zinc zinc Melt IndexD-1238 g/10 min. 2.8 0.8 1.5 2.5 Density D-1505 kg/m³ 960 960 960 960Melting Point D-3417 ° C. 87.5 90 90 90 Crystallization D-3417 ° C. 55 —— — Point Vicat Softening D-1525 ° C. 67 60 63 62.5 Point % Weight — — —— Acrylic Acid % of Acid — — — — Groups Cation Neutralized PlaqueProperties (3 mm thick, compression molded) Tensile at D-638 MPa 28 3838 38 Break Yield Point D-638 MPa 23 none none Elongation at D-638 % 395500 420 395 Break 1% Secant D-638 MPa 390 — — — modulus Shore HardnessD-2240 — 59 57 55 55 D

In addition to the above noted ionomers, compatible additive materialsmay also be added to produce the cover compositions of the presentinvention. These additive materials include dyes (for example,Ultramarine Blue sold by Whitaker, Clark, and Daniels of SouthPainsfield, N.J.), and pigments, i.e. white pigments such as titaniumdioxide (for example Unitane 0-110) zinc oxide, and zinc sulfate, aswell as fluorescent pigments. As indicated in U.S. Pat. No. 4,884,814,the amount of pigment and/or dye used in conjunction with the polymericcover composition depends on the particular base ionomer mixtureutilized and the particular pigment and/or dye utilized. Theconcentration of the pigment in the polymeric cover composition can befrom about 1% to about 10% as based on the weight of the base ionomermixture. A more preferred range is from about 1% to about 5% as based onthe weight of the base ionomer mixture. The most preferred range is fromabout 1% to about 3% as based on the weight of the base ionomer mixture.The most preferred pigment for use in accordance with this invention istitanium dioxide.

Moreover, since there are various hues of white, i.e. blue white, yellowwhite, etc., trace amounts of blue pigment may be added to the coverstock composition to impart a blue white appearance thereto. However, ifdifferent hues of the color white are desired, different pigments can beadded to the cover composition at the amounts necessary to produce thecolor desired.

In addition, it is within the purview of this invention to add to thecover compositions of this invention compatible materials which do notaffect the basic novel characteristics of the composition of thisinvention. Among such materials are antioxidants (i.e. Santonox R),antistatic agents, stabilizers and processing aids. The covercompositions of the present invention may also contain softening agents,such as plasticizers, etc., and reinforcing materials such as glassfibers and inorganic fillers, as long as the desired properties producedby the golf ball covers of the invention are not impaired.

Furthermore, optical brighteners, such as those disclosed in U.S. Pat.No. 4,679,795, may also be included in the cover composition of theinvention. Examples of suitable optical brighteners which can be used inaccordance with this invention are Uvitex OB as sold by the Ciba-GeigyChemical Company, Ardsley, N.Y. Uvitex OB is thought to be2,5-Bis(5-tert-butyl-2-benzoxazoly)thiophene. Examples of other opticalbrighteners suitable for use in accordance with this invention are asfollows: Leucopure EGM as sold by Sandoz, East Hanover, N.J. 07936.Leucopure EGM is thought to be7-(2n-naphthol(1,2-d)-triazol-2yl)-3phenyl-coumarin. Phorwhite K-20G2 issold by Mobay Chemical Corporation, P.O. Box 385, Union Metro Park,Union, N.J. 07083, and is thought to be a pyrazoline derivative,Eastobrite OB-1 as sold by Eastman Chemical Products, Inc. Kingsport,Tenn., is thought to be 4,4-Bis(-benzoxaczoly)stilbene. Theabove-mentioned Uvitex and Eastobrite OB-1 are preferred opticalbrighteners for use in accordance with this invention.

Moreover, since many optical brighteners are colored, the percentage ofoptical brighteners utilized must not be excessive in order to preventthe optical brightener from functioning as a pigment or dye in its ownright.

The percentage of optical brighteners which can be used in accordancewith this invention is from about 0.01% to about 0.5% as based on theweight of the polymer used as a cover stock. A more preferred range isfrom about 0.05% to about 0.25% with the most preferred range from about0.10% to about 0.020% depending on the optical properties of theparticular optical brightener used and the polymeric environment inwhich it is a part.

Generally, the additives are admixed with a ionomer to be used in thecover composition to provide a masterbatch (M.B.) of desiredconcentration and an amount of the masterbatch sufficient to provide thedesired amounts of additive is then admixed with the copolymer blends.

The above cover compositions, when processed according to the parametersset forth below and combined with soft cores at thicknesses definedherein to produce covers having a Shore D hardness of 65, provide golfballs with reduced spin ratio. It is noted, however, that the high acidionomer resins provide for more significant reduction in spin rate thanthat observed for the low acid ionomer resins.

The cover compositions and molded balls of the present invention may beproduced according to conventional melt blending procedures. In thisregard, the ionomeric resins are blended along with the masterbatchcontaining the desired additives in a Banbury type mixer, two-roll mill,or extruded prior to molding. The blended composition is then formedinto slabs or pellets, etc. and maintained in such a state until moldingis desired. Alternatively a simple dry blend of the pelletized orgranulated resins and color masterbatch may be prepared and fed directlyinto the injection molding machine where homogenization occurs in themixing section of the barrel prior to injection into the mold. Ifnecessary, further additives such as an inorganic filler, etc., may beadded and uniformly mixed before initiation of the molding process.

Moreover, golf balls of the present invention can be produced by moldingprocesses currently well known in the golf ball art. Specifically, thegolf balls can be produced by injection molding or compression moldingthe novel cover compositions about the soft polybutadiene cores toproduce a golf ball having a diameter of about 1.680 inches or greaterand weighing about 1.620 ounces. In an additional embodiment of theinvention, larger molds are utilized to produce the thicker coveredoversized golf balls.

As indicated, the golf balls of the present invention can be produced byforming covers consisting of the compositions of the invention aroundthe softer polybutadiene cores by conventional molding processes. Forexample, in compression molding, the cover composition is formed viainjection at about 380° F. to about 450° F. into smooth surfacedhemispherical shells which are then positioned around the core in adimpled golf ball mold and subjected to compression molding at 200-300°F. for 2-10 minutes, followed by cooling at 50-70° F. for 2-10 minutes,to fuse the shells together to form an unitary ball. In addition, thegolf balls may be produced by injection molding, wherein the covercomposition is injected directly around the core placed in the center ofa golf ball mold for a period of time at a mold temperature of from 50°F. to about 100° F. After molding the golf balls produced may undergovarious further finishing steps such as buffing, painting, and markingas disclosed in U.S. Pat. No. 4,911,451.

The present invention is further illustrated by the following examplesin which the parts of the specific ingredients are by weight (pbw). Itis to be understood that the present invention is not limited to theexamples, and various changes and modifications may be made in theinvention without departing from the spirit and scope thereof.

EXAMPLE 1

Using the ingredients tabled below, golf ball cores having a finisheddiameter of about 1.540 to about 1.545 inches were produced bycompression molding and subsequent removal of a surface layer bygrinding. Each core was formulated using 100 parts elastomer (rubber).In the formulations, the amounts of remaining ingredients are expressedin parts by weight, and the weight, degrees of coefficient ofrestitution and compression (both Riehle and PGA) achieved are set forthbelow. The data for these examples are the averages for twelve coreswhich were produced for each example. The properties of the molded coresproduced from each formulation were measured according to the followingparameters:

Riehle compression is a measurement of the deformation of a golf ball inthousandths of inches under a fixed static load of 200 pounds (a Riehlecompression of 47 corresponds to a deflection under load of 0.47inches).

PGA compression is determined by a force applied to a spring (i.e. 80PGA=80 Riehle; 90 PGA=70 Riehle; and 100 PGA=60 Riehle) and manufacturedby Atti Engineering, Union City, N.J.

Coefficient of restitution (C.O.R.) was measured by firing the resultinggolf ball in an air cannon at a velocity of 125 feet per second againsta steel plate which is positioned 12 feet from the muzzle of the cannon.The rebound velocity was then measured. The rebound velocity was dividedby the forward velocity to give the coefficient of restitution.

The following core formulations were prepared according to the methodsset forth above:

CORE COMPOSITIONS A B C D Ingredients BR-1220¹ 100 100 100 100 ZincDiacrylate 18 20 37 26 Ground Flash 17 20 20 17 Zinc Oxide 6 6 6 6Limestone 7 25 15 — Zinc Stearate 15 20 20 15 6400 Polypropylene² 10 — —10 Trigonox 17/40³ 1.5 1.5 1.5 1.5 Papi 94⁴ 0.5 0.5 0.5 0.5 Molded CoreProperties Core Diameter (in.) 1.541 1.542 1.543 1.542 Weight (grams)33.7 36.5 36.8 33.8 Compression (Riehle/PGA) 87/73 83/77 64/96 74/86C.O.R. ({overscore (e)}) .773 .782 .802 .787 ¹BR-1220 is a polybutedienemanufactured and sold by Shell Chemical Co., Houston, Texas. ²6400 P. isa powdered polypropylene available from Amco Chemical Co., Chicago,Illinois. ³Trig 17/40 is a peroxide manufactured and sold by AkzoChemie, Chicago, Illinois (one hour half life is at 129° C.). ⁴Papi 94is a polymeric diisocynanote available from Dow Chemical Co., Midland,Michigan.

As noted by the above indicated data, core formulations A and B producesofter cores. Formulation A is appropriate for a molded ball having anoverall diameter of about 1.720 inches (i.e., 1.717″). It has lessfiller, hence a lower specific gravity, than formulation B which isappropriate for a smaller ball, one having a diameter of about 1.680inches. Formulations C and D are for conventional harder cores.Formulation C is slightly heavier and used for a ball having a diameterof about 1.680 inches. Formulation D is used for producing a ball havinga diameter of about 1.720 inches (1.717″).

EXAMPLE 2

Cover compositions were produced by blending the following constituents:

COVER COMPOSITIONS Ingredients Cover 1 Cover 2 Cover 3 Iotek 8000 45.2 —22.6 Iotek 7030 45.2 — 22.6 Iotek 959 — 45.2 — Iotek 960 — 45.2 — Iotek7520¹ — — 45.2 White MB²  9.6  9.6  9.6 ¹Iotek 7520 is a relativelysoft, low acid, ionomer resin produced by Exxon. ²MB = 74.9 wt-% Iotek7030, 23.8 wt-% TiO₂, 0.01 wt-% Unitex O8, 0.002 wt-% ultra marine blueand 300 ppm Sontonox R.

Of the three cover formulations provided above, formulation 2 is thehardest. It is comprised of two hard, high acid ionomer resins. Iotek959 has an acid content of about 19% to 21% and Iotek 960 also has anacid content of about 19 to 21%.

Formulation 3 provides the softest of the three cover formulations andis substantially similar to the formulation used in the TOP-FLITE TOUREDITION 90 golf ball. Formulation 3 is comprised of Iotek 8000 and Iotek7030, both hard, low acid ionomers, and Iotek 7520, a soft, low-acidionomer, in the amounts set forth above.

Formulation 1 provides intermediate hardness, and is essentially thesame formulation used in the TOP FLITE XL II ball (see U.S. Pat. No.4,911,481).

EXAMPLE 3

The cover formulations set forth in Example 2 were injection molded atabout 400° F. around cores of formulations A-D in Example 1 in a mannerto permit uniform injection of the selected cover composition over eachcore. Each of the cores had an identical finished diameter of about1.541-1.543 inches to produce golf balls of approximately 1.720 (1.717)inches (cores A and D) or about 1.680 inches (cores B and C) indiameter. The cover thickness varied between about 0.069 and about 0.088inches. All materials were molded under essentially identicalconditions. The properties of Riehle compression, PGA compression,coefficient of restitution (C.O.R.), barrel durability (100 blows),cover hardness and spin rate were determined. The results are set forthin Table 3 below.

The data for each example represents the average data for one dozenballs produced according to the desired manner. The properties weremeasured according to the following parameters:

Coefficient of restitution (C.O.R.) was measured by firing the resultinggolf ball in an air cannon at a velocity of 125 feet per second againsta steel plate which is positioned 12 feet from the muzzle of the cannon.The rebound velocity was then measured. The rebound velocity was dividedby the forward velocity to give the coefficient of restitution.

Shore hardness was measured in accordance with ASTM Test D-2240.

The barrel test or barrel durability test involves firing golf balls at135 ft./sec. (at 72° F.), into a 5-sided container, the walls of whichare steel plates that have grooves milled into them to simulate a golfclub face. The balls are subjected to 100 to 300 blows and are inspectedat regular intervals for breakage (i.e. any signs of cover cracking ordelamination). NB=no breakage.

The spin rate of the golf ball was measured by striking the resultinggolf balls with a 9-iron wherein the club-head speed is about 105 feetper second and the ball is launched at an angle of 26 to 34 degrees withan initial velocity of about 110-115 feet per second. The spin rate wasmeasured by observing the rotation of the ball in flight using stopaction Strobe photography.

TABLE 3 Barrel Cover Spin Rate Ball/Type Ball Riehle PGA DurabilityHardness #9 Iron (Core/Cover) Size Comp. Comp. C.O.R. (100 blows) ShoreC/D (105 fps) A, 1 1.72 62 98 .814 NB 96/65 7019 A, 2 1.72 59 101 .827NB 97/68 6544 A, 3 1.72 65 95 .795 NB 87/56 8409 B, 1 1.68 61 99 .793 NB95/65 7541 B, 2 1.68 57 103 .803 NB 97/68 6755 B, 3 1.68 62 98 .775 NB87/56 8764 C, 1 1.68 49 111 .816 NB 95/65 7643 C, 2 1.68 47 113 .822 NB97/68 6933 C, 3 1.68 50 110 .805 NB 87/56 9231 D, 1 1.72 57 103 .820 NB95/65 7285 D, 2 1.72 55 105 .830 NB 97/68 6816 D, 3 1.72 58 102 .802 NB87/56 8578

For comparison purposes, the same results are provided for knownpreexisting golf balls:

Barrel Cover Spin Rate Ball/Type Ball Riehle PGA Durability Hardness #9Iron (Core/Cover) Size Comp. Comp. C.O.R. (100 blows) Shore C/D (105fps) Titleist Tour 100 1.68 73 87 .792 NB 83/51 9676 Tour Edition 1001.68 58 102 .802 NB 85/53 9961 Tour Edition 90 1.68 56 104 .802 NB 87/569621 Top-Flite XL II 1.68 51 109 .810 NB 95/65 7163

Molded ball spin test results show that notwithstanding differences inball size, the combination of a soft core (cores A and B) with a hardcover (cover formulations 1 and 2) minimizes spin rate. Even in theinstance where harder cores are used (cores C and D) the golf ball withthe hardest cover formulation tested (formulation 2) provides for golfballs having the lowest spin rate.

Further reduction in spin rate is observed through the use of a softcore (core A and B) with the hardest cover (cover formulation 2), withthe largest reduction in spin rate observed through the use of thesoftest core (core A) with the hardest cover (cover formulation 2).

It should be further noted that increased diameter provides for lowerspin rates. In comparing balls A,1-3 with corresponding balls B,1-3, theballs having the larger diameter (A,1-3) are lower in spin than ballsB,1-3, respectively. The C.O.R. and compression are controlled mainly bythe core formulation, with a hard fast core giving a harder, fasterball.

As ball diameter increases upon increasing the cover thickness (corediameter remains the same), the thicker cover (0.0888 versus 0.0690inches) provides for significant C.O.R. pickup from center to ball.Further, the increased cover thickness plays a role in added spinreduction observed for the larger balls.

With attention still focused on the tabulated results, the combinationof a soft core with a hard cover gives the lowest spin. In comparingball A,2 to ball D,2 (both at 1.72 inches in diameter) it is seen thatthe softer core A contributes to lower spin rates. Combination A,2(softer core, hardest cover) provides the lowest spin rate for theentire test. These same trends hold for the smaller balls, i.e. ball B,2is lower in spin that ball C,2. While ball B,2 is the lowest spin amongthe 1.68 inch balls, its spin rate is not as low as ball A,2 which has alarger diameter. This is believed to be attributed to the differences incover thickness.

The invention has been described with reference to the preferredembodiment. obviously, modifications and alterations will occur toothers upon a reading and understanding of the preceding detaileddescription. It is intended that the invention be construed as includingall such alterations and modifications insofar as they come within thescope of the appended claims or the equivalents thereof.

Having thus described the invention, it is claimed:
 1. A golf ball,comprising: a core comprising a diene polymer having a Riehlecompression of at least 0.075 inches; and a cover having a Shore Dhardness of at least 65, wherein the cover is comprised of at least onehigh acid ionomer resin comprising a copolymer of greater than 16% byweight of an acrylic acid, and an alpha olefin of which about 10 toabout 90% of the carboxyl groups of the copolymer are neutralized with ametal cation.
 2. A golf ball, as set forth in claim 1, wherein the coveris comprised of at least one high acid ionomer resin comprising acopolymer of about 17% to about 25% by weight of an acrylic acid, and analpha olefin of which about 10 to about 90% of the carboxyl groups ofthe copolymer are neutralized with a metal cation.
 3. A golf ball, asset forth in claim 1, wherein the cover is comprised of at least onehigh acid ionomer resin comprising from about 18.5% to about 21.5% byweight of an acrylic acid, and an alpha olefin of which about 10 toabout 90% of the carboxyl groups of the copolymer are neutralized with ametal cation.
 4. A golf ball, as set forth in claim 1 wherein the coreis comprised of polybutadiene, at least one metallic salt of anunsaturated carboxylic acid and a free radical initiator.
 5. A golfball, as set forth in claim 1, wherein the cover has a thickness greaterthan 0.0675 inches.
 6. A golf ball, as set forth in claim 1, wherein thecover has a thickness greater than 0.0675 inches to 0.130.
 7. A golfball, as set forth in claim 1, wherein the golf ball has a diameter ofabout 1.680 to 1.800 inches.
 8. A golf ball, as set forth in claim 1,wherein the golf ball has a diameter of about 1.700-1.800 inches.
 9. Agolf ball, as set forth in claim 1, wherein the golf ball has a diameterof about 1.710-1.730 inches.
 10. A golf ball, as set forth in claim 1,wherein the golf ball has a diameter of about 1.717-1.720 inches.
 11. Amolded golf ball comprising a core and a cover, wherein said corecomprises a dicnc polymer and has a Riehle compression of about 0.075 to0.115 inches, and wherein said cover has a Shore D hardness of at least65, a thickness of about 0.0675 to 0.130 inches and is comprised of atleast one high ionomeric resin comprising at least 16% by weight acrylicacid and an alpha olefin of which about 10 to about 90% of the carboxylgroups of the copolymer are neutralized with a metal cation.
 12. Amolded golf ball, as set forth in claim 11, wherein the core has aRiehle compression of 0.080 to 0.090, and a diameter of about1.540-1.545 inches.
 13. A molded golf ball, as set forth in claim 11,wherein the molded golf ball has a diameter of about 1.70-1.80 inches.14. A molded golf ball, as set forth in claim 11, wherein the moldedgolf ball has a diameter of about 1.710-1.730 inches.
 15. A molded golfball, as set forth in claim 11, wherein the molded golf ball has adiameter of about 1.717-1.720 inches.
 16. A molded golf ball,comprising: a core having a Riehle compression of at least 0.075 inchesand a diameter of about 1.540-1.545 inches; and a cover having comprisedof at least one ionomer resin including a copolymer of about 17% toabout 25% by weight of an acrylic acid, and an alpha olefin of whichabout 10 to about 90% of the carboxyl groups of the copolymer areneutralized with a metal cation, said cover having a thickness of about0.0675 to 0.1275 inches and a Shore D hardness of at least about
 65. 17.The molded golf ball of claim 16 wherein said core comprises 100 partsby weight polybutadiene, from about 15 to about 25 parts by weight of atleast one metallic salt of an unsaturated barboxylic acid and about 0.1to about 5.0 parts by weight of a free radial initiator.